1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a reflective liquid crystal display device having high reflectivity and a method for manufacturing the same.
2. Discussion of the Related Art
A typical liquid crystal display (LCD) device is provided with lower and upper substrates facing each other at a predetermined distance, and a liquid crystal layer formed between the lower and upper substrates. The liquid crystal layer is driven by an electric field formed between the lower and upper substrates, so that the light transmittance is controlled, thereby displaying an image on an LCD panel. However, the LCD device does not emit light by itself, so that a backlight is additionally required to display the image on the LCD panel, or natural light is used as a light source to the LCD device.
In general, the LCD device is classified into two types, i.e., a transmissive liquid crystal display device using the backlight as the light source, and a reflective liquid crystal display device using the natural light as the light source. The transmissive liquid crystal display device has limitations in that it is hard to obtain ultra-thinness and lightness due to the weight and volume of the backlight. Also, power consumption increases since the backlight is driven. Accordingly, many efforts have been made to study the reflective liquid crystal display (LCD) device using natural light as the light source.
A related art reflective LCD device will be explained with reference to the accompanying drawings.
FIG. 1A is a plan view illustrating a unit pixel in a lower substrate of a related art reflective LCD device. FIG. 1B is a sectional view illustrating a unit pixel in a lower substrate of a related art reflective LCD device according to the present invention taken along line A—A of FIG. 1A. Although not shown, a plurality of pixels are formed in a matrix type at left and bottom sides in the context of FIG. 1A.
As shown in FIG. 1A and FIG. 1B, a plurality of gate lines 12 are horizontally formed on a lower substrate 10, and a gate pad 12a is formed at each one end of the gate lines 12. A plurality of gate electrodes 14 are projected from the gate line at a predetermined interval. A gate insulating layer 16 is formed on an entire surface of the lower substrate, and a semiconductor layer 18 is patterned on the gate insulating layer 16. Then, a plurality of data lines 20 are formed to cross the plurality of gate lines 12, thereby defining a plurality of pixel regions. At this time, a data pad 20a is formed at each one end of the data lines 20, and source/drain electrodes 22 and 24 are formed on the same layer as the data line 20. The source/drain electrodes 22 and 24 are patterned on the semiconductor layer 18, thereby forming a thin film transistor (TFT) with the gate electrode 14.
A passivation layer 26 is formed on the entire surface of the lower substrate, and reflective electrodes 30 and 30a are formed on the passivation layer 26. At this time, the reflective electrode 30 is connected to the drain electrode 24 of the thin film transistor through a contact hole formed in the passivation layer 26 (not labeled). Also, the reflective electrode 30a is connected to the gate pad 12a and the data pad 20a through a contact hole (not labeled) formed in the passivation layer 26 and the gate insulating layer 16. In general, the reflective electrodes 30 and 30a are made of Aluminum (Al) having high reflectivity and high transmittance.
In order to achieve the LCD device having high luminance, it is necessary to form the reflective electrode having high reflectivity. The reflective electrode being made of aluminum (Al) may deform during a heat treatment process due to a poor heat-resistance of aluminum (Al). Accordingly, the reflective electrode has to be made of a material having high heat-resistance and high reflectivity.